Autoimmune hepatitis (AIH) is a chronic portal inflammation of unknown etiology that can lead to cirrhosis and liver failure if not properly controlled. Current treatment of AIH relies on long-term systemic immune suppression. However, such therapy places patients at risk of severe side effects;moreover, a significant minority does not respond. The lack of a robust animal model for the disease has hampered progress in understanding the pathogenesis of this disease and improving diagnosis and treatment. Diacylglycerol kinases (DGKs) catalyze the conversion of diacylglycerol to phosphatidic acid through phosphorylation. We and others have recently demonstrated that DGKa and ?, isoforms expressed in T cells, negatively control T cell activation by inhibiting T cell receptor (TCR)-induced Ras and Erk1/2 activation. Deficiency of either DGKa or ? causes T cells to be hyperresponsive to TCR stimulation and resistant to anergy induction. Our central hypotheses for this application are that DGKa and ? synergistically contribute to self-tolerance to the liver and that loss of T cell-tolerance and dysfunction of regulatory T cells (Tregs) contributes to the pathogenesis of AIH. With strong preliminary data, we plan to use DGKa and ? doubly deficient (DGKa? DKO) mice to test our central hypotheses by pursuing three specific aims. In Aim 1, we will define DGKa? DKO mice as a relevant model for chronic AIH and liver fibrosis. In Aim 2, we will determine the role of T cell subsets in the pathogenesis of hepatitis in DGKa? DKO mice. In Aim 3, we will determine the signaling mechanisms that participate in the pathogenesis of AIH. The proposed studies should establish DGKa? DKO mice as a proper model for chronic AIH and liver fibrosis, improve understanding of the mechanisms involved in the pathogenesis of AIH, and provide new therapeutic strategies for the disease. Public Health Relevance: This grant application aims to establish a long-awaited murine model of chronic autoimmune hepatitis and liver fibrosis and is directly relevant to FOA PA-07-012 entitled 'Animal Models of NIDDK Relevant Diseases'and to the NIDDK Liver Diseases Research Action Plan. The proposed studies are expected to improve understanding of the pathogenesis of autoimmune hepatitis and provide therapeutic strategies for AIH and other autoimmune diseases.